The long-term goal of our laboratory is to understand how specific protein kinase signaling pathways and phosphoserine/threonine-binding domains regulate cell cycle progression and the response to DNA damage. In response to genotoxic stress, cells activate two canonical protein kinase pathways, the ATR-Chk1 pathway, and the ATM-Chk2 pathway. We recently identified a third DNA damage response pathway mediated by p38MAPK and MAPKAP Kinase-2 (MK2) that is absolutely essential for p53-defective tumor cells to survive after DNA damage. Importantly, this pathway is largely dispensable in cells with intact p53 function, making it an ideal target for specifically impairing the DNA damage response in cancer cells. Furthermore, unlike the ATR-Chk1 and ATM-Chk2 pathways that are dedicated to responding solely to signals from DNA damage per se, the p38 MAPK-MK2 pathway is a much more global stress-response pathway that can also be activated by other types of cellular stress, and plays a critical role in cytokine production during inflammation and tumorigenesis Thus, we believe that the p38MAPK-MK2 pathway plays a particularly novel role during oncogenic and genotoxic stress by integrating DNA damage response pathways within tumor cells with inflammation and cytokine signaling in the adjacent tumor microenvironment. In this proposal we define the role of MK2 in both tumor development and therapeutic response using novel conditional knock-out mouse models, identify the molecular mechanism by which MK2 regulates the G1/S checkpoint, and define its role in post-transcriptional regulation of gene expression through phosphorylation of RNA-binding proteins, which we then explore through a structural and mechanistic approach. Finally, we identify new MK2, Chk1 and Chk2 substrates involved in cell cycle control and DNA damage responses. Data emerging from the proposed experiments should (1) substantially enhance our understanding of the roles of tumor- and stromal derived MK2 in cancer development and progression, (2) expand our knowledge of signaling pathways that control environmental risk for cancer, and (3) identify and validate new molecular targets against which both cancer prevention strategies and anti-cancer therapies can be designed, including MK2 itself and RNA-binding proteins.